FTB 06-13-2018: Battle Between Dry Air and Moist Air

Issue Date: 6/13/2018
Issue Time: 8:12 AM


Colorado is ground-zero for a battle between dry air and moist air, both in the mid-levels and at the surface. Shown in the water vapor imagery below is the mid-level battle, where moist air from the south is attempting to nudge northward into western Colorado. This moist air will make a valiant effort, pushing north towards I-70 over the High Country and Western Slope. This moisture will be sufficient enough to produce isolated, high-based showers/thunderstorms over southern and central portions of the High Country, producing very little rain (if any), with plenty of lightning and virga painting the sky.

The battle in the low-levels will take place east of the mountains, where east-southeasterly flow has pushed moisture rich low-level air into eastern Colorado. Dry air from the west will try to scour this moisture, with a dry line setting up along, or just east of, the foothills. The moisture, combined with daytime heating, will be enough to produce isolated-to-scattered thunderstorms, with the best coverage and intensity occurring east of I-25. A couple of the storms will become severe, with the potential to produce hail up to 1.5-2 inches in diameter and strong winds greater than 55 mph.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below (hover over threat areas for more details). For Zone-Specific forecasts, jump below the map.

Flood Threat Legend

Zone-Specific Forecasts

Front Range, Urban Corridor, Palmer Ridge, Northeast Plains, Southeast Plains, and Raton Ridge:

Isolated-to-scattered thunderstorms will rumble today/tonight. Without a “trigger” in the mid-/upper-levels, it will be up to low-level convergence and daytime heating to produce adequate forcing for thunderstorm development. With south-southeasterly winds at the surface, the Denver cyclone is expected to aid thunderstorm development, likely kicking off a couple thunderstorms in the vicinity of the Denver metro area. Most storms will struggle to produce heavy rain thanks to dry air in the mid-levels zapping some of the potential, but hail clogging drainage and brief periods of heavy rainfall will likely produce a couple instances of street/field ponding in poorly drained areas. This is the culprit behind the low flood threat. Maximum rain rates are as follows:

Front Range: 0.05-0.25 inches/hour
Urban Corridor, Palmer Ridge, and Raton Ridge: 0.5-1.0 inches/hour
Northeast Plains and Southeast Plains: 1.0-1.5 inches/hour

Timing: 2 PM – 11 PM, with a couple lingering thunderstorms over the Northeast and Southeast Plains until 2 AM

Northern Mountains, Northwest Slope, Central Mountains, Grand Valley, San Juan Mountains, Southeast Mountains, San Luis Valley, and Southwest Slope:

Dry and hot will be the main weather story today, with only a few isolated, high-based thunderstorms rumbling during the afternoon and evening hours south of I-70 where mid-level moisture from the south can have an impact. Dry air in the low-levels will keep rain rates low, so no flash flooding is expected. Maximum rain rates will be 0.05-0.10 inches/hour. North of I-70, expect dry conditions and mostly sunny skies to rule the day.

Timing: 1 PM – Midnight